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Hoofdstuk 12. Control Structures
Elk PHP script bestaat uit reeksen van statements. Een statement
kan een assignment, een functie aanroep, een loop, een conditional
statement of zelfs een statement zijn dat niets doet (een empty
statement). Statements eindigen gewoonlijk met een puntkomma.
Als toevoeging hierop kunnen statements gegroepeerd worden tot een
statement-groep door deze te omvatten met accolades. Een statement-groep
is een statement op zichzelf. De overige statements zijn beschreven in
dit hoofdstuk.
if
De if constructie is ��n van de
meest belangrijkste in veel talen, zoals ook in PHP. Het maakt het
mogelijk om stukken code conditioneel uit te voeren. PHP heeft een
if structuur die gelijk is als die van de taal C.
Zoals is beschreven in de sectie over expressies, wordt
"expressie" geevalueerd naar zijn "truth" waarde.
Als de expressie
evalueert tot TRUE, dan zal PHP het statement uitvoeren,
en als de expressie evalueert naar FALSE, dan zal het
statement worden overgeslagen.
Het volgende voorbeeld zal bijvoorbeeld tonen a is groter
dan b indien $a groter is
dan $b:
Vaak zul je willen dat er meer dan ��n statement
conditioneel wordt uitgevoerd. Natuurlijk hoef je niet elk
statement met een if clause te omvatten. In
plaats daarvan kun je een meerdere statements tot een
statement groep maken. De code in het volgende voorbeeld zal
tonen a is groter dan b
als $a groter is dan
$b, en het zal de waarde van de variabele
$a naar $b
kopie�ren:
If statements kunnen oneindig worden genest binnen andere
if statements. Dit geeft je de complete flexibiliteit
voor conditionele uitvoering van verschillende delen van je programma.
User Contributed Notes
Control Structures |
 add a note |
lexzeus at mifinca dot com
08-Nov-2000 05:14 |
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function lex1()
{
print "Hello";
return
1;
}
function lex2()
{
print "World";
return
1;
}
if (lex1() || lex2()) {}
it only print
"Hello", so lex2() never been executed.
So, u can also
write :
if (
@function1() &&
@function2()
&&
@function3() &&
@function4()
&&
@function5()) {}
It will do all functions from
1 to 5 but terminated immediately if one of the function is
failed.
LexZEUS
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14-Feb-2002 03:20 |
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for beginners like me!
don't forget that if you want a=b, it has to be
a==b
for example
<?
$a=2;
$b=2;
if ($a==
$b)
echo "that's right!";
?>
and read the
manual!
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adolfoabegg at hotmail dot com
26-Mar-2002 10:15 |
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You can also use this syntax:
(it worked out for me)
if
(conditional):
//sentences
elseif(conditional2):
//sentences
else:
//more
sentences
endif;
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maurizio at zilli dot com
11-Apr-2002 09:14 |
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You can also use this if/else condition structure
to control an index
navigation page statement
and extract partial rows from an
array.
// Init to control pointer into the array
$setlimit =
10; // rows limit
$pointer = 0; // this is the start pointer
value
$next = $pointer + $setlimit; // increment the pointer
$prev=
$next - $setlimit; // decrement the pointer
$total_rows =
mysql_num_rows($myrows); // total rows
// You're at the
beginning
if (($pointer == 0) && ($total_rows >
$setlimit)):
echo"$next >>";
// You're in
the middle
elseif ($next < $total_rows):
echo"<<
$prev";
echo"$pointer";
echo"$next
>>";
// You're in a selection with only one
row
elseif (($next == $total_rows) && ($next >
$total_rows)):
// You're at the
end
else:
echo"<< $prev";
endif;
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simon at invalid dot com
20-Aug-2002 07:11 |
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There are something to remind beginners:
if(-1)
echo "(-1
OK) ";
else
echo "(-1 fail)
";
if("")
echo "(\"\" OK)
";
else
echo "(\"\" fail)
";
if(0)
echo "(0 OK) ";
else
echo "(0
fail) ";
// result: (-1 OK) ("" fail) (0
fail)
In addition, if you want check if $a,$b and $c are all the
same, you should have the condition like that:
if($a==$b &&
$a==$c) {
//do somthing;
}
else {
//do
something;
}
Moreover, in (condition1 && condition2), if
condition1 is FALSE, then condition2 will not be checked/executed, in the
case, if want to executed condition2, use (condition1 & condition2)
instead
The case is similar in (condition1 || condition2), if you
want to execute condition2 no matter condition1 is TRUE or not, use
(condition1 | condition2)
Hope can help you
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simon at blueshell.dk
09-Sep-2002 09:30 |
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[Editor's note: It would be better practice to use the ternary operator as
argument for the "print" language construct, e.g.:
print ($foo == $bar) ? "The match" : "They don't
match";
Same approach can be used for
assignment.]
For short if-else's:
if ($foo == $bar)
{
print "They match";
} else {
print "They
don't match";
}
This can quickly be converted
into:
($foo == $bar) ? print "They match" : print
"They don't match";
This can be useful if the check's
intention can be expressed in matter of a single function, like this.
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php dot net at popquizhotshot dot com
10-Dec-2002 01:10 |
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I've noticed the following behaviour:
echo (1==1) ? "true"
: "false";
and
echo "anything here at all" .
(1==1) ? "true" : "false";
produce the exact
same (unexpected to me) result:
true
"anything here at
all" is dropped.
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Matt Stanley
13-Feb-2003 04:01 |
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you can use
echo 'anything here at all' , (1==1) ? 'true' :
'false';
instead. Plus as an extra bonus, its a little faster
(for simple text)
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16-Feb-2003 10:23 |
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An item that should be added to the Table of Contents on this
page:
exit
And for its description (on a new
page):
exit�--�Terminate all script execution for this request.
(For HTTP requests, this causes the response generated thus far to be sent
to the browser.)
Use "return" to terminate the current
script only and return to any script that included it (resuming execution
at the point after the include).
"exit" can be used
immediately following a "require" or "include" to
simulate unconditional branching (i.e. "go to") to another
script file.
"Exit" is a language construct but is often
treated as a function. The parentheses are unnecessary unless a status
needs to be returned.
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ian at iyates dot com
24-Mar-2003 05:26 |
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In response to LexZEUS:
If you used the same code with | instead of
|| and & instead of && (as follows)
function
lex1()
{
print "Hello";
return 1;
}
function
lex2()
{
print "World";
return 1;
}
if (lex1() |
lex2()) {}
if (
@function1() &
@function2()
&
@function3() &
@function4() &
@function5()) {}
All functions would be executed before the final
boolean is returned.
Although || and && are more useful
(efficient and easy to understand), | and & are normally used when
some functions _have_ to be executed even if one fails.
a good
example is:
if (isset($a) && $a == 'hello')
echo
$a;
if (isset($b) & $b == 'world')
echo $b;
while
the first 'if' will always be okay, the second will return an error if $b
had not been set as it will still compare $b to 'world' (which should
return 'false' and a warning)
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kriek at jonkriek dot com
29-Mar-2003 02:06 |
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It should be noted that in MOST cases it is fifteen percent faster to use
switch/case/break instead of if/elseif/else. Of course this depends on
your application and individual code results do very.
<?php
if ($_GET['page']) {
$page = $page . '.php';
if (file_exists($page)) {
include($page);
}
} else {
include('welcome.php');
}
if
($_GET['auc']) {
$auc = $auc . '.html';
if
(file_exists($auc)) {
include($auc);
}
} else {
include('welcome.html');
}
?>
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Storm
04-May-2003 12:16 |
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Although the alternate syntax is nice, I myself prefer to use a simple
function:
function iif ($statement,$true_return,$false_return)
{
if ($statement == false) {
return $false_return;
} else {
return $true_return;
}
}
Works great
for me...
$one = iif (isset($one),$one,'one');
$two = iif
(isset($two),$two,'two');
$three = iif
(isset($three),$three,'three');
:D
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armond A.T technoREM0VEmonk d0t com
14-May-2003 06:02 |
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From my tests, some more complex if() statements may not have desired
results.
Take for instance,
$a = 79;
$b = 82;
$c =
40;
if($c == ($a || $b)) { ... }
You would think that would be
stating:
"If $c equals $a or $b"
And would return false,
but think again.
I have an idea of whats going on here-its equating
it like a matematical equasion, and we follow the EPMDAS order.
I
haven't found a workaround, so for now we're stuck to:
if($c == $a ||
$c == $b) { .. }
Armond Carroll
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add a note |
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PHP Handleiding
Syntax
Basis syntax
Control Structures
Array Operators